Warning systems, which warn the driver when he leaves the lane, or rather, threatens to leave the lane, are known in the related art. European Published Patent Application No. 1074430, for example, shows a procedure in which, based on image sensor systems, the lane in which the vehicle is moving is ascertained, and the driver is warned when the vehicle leaves the lane or threatens to do so. Information on the exact boundary conditions, under which such a warning is given, is not stated. In particular, the respective driving situation is not taken into consideration, so that disagreeable false warnings to the driver may occur.
From German Published Patent Application No. 196 37 053 it is known that one may detect objects on a neighboring traffic lane, with the aid of an angle-resolving distance and speed sensor, preferably a radar or laser sensor, and ascertain their travel direction in the light of the relative speed of these objects.